1. Technical Field
This invention relates to metal corrosion and in particular corrosion due to interaction with chlorine or sulfur containing entities.
2. Art Background
Metals such as copper, nickel, and silver are extremely important for their use in a vast number of applications. Not only are such metals used for their aesthetic appeal in ornamental objects but also a large number of industries, such as the electronics industry, rely extensively on these materials because of their electrical and structural properties. Whether the metals are used for ornamental purposes, structural purposes, or for high technology products, corrosion, e.g., sulfidization or chlorination, of the metal surface seriously degrades is usefulness for many desired applications. A variety of expedients have been developed to either prevent or impede the corrosion of metals, e.g., metals utilized in ornamental objects or structures employed in electronic industries. For example, these objects have been enclosed in a wrapper where the wrapper itself or an object placed within the wrapper contains volatile organic corrosion inhibitor (VCI). The VCI such as cyclohexamine ammonium benzoate, evaporates, coats the metal to be protected and thus produces corrosion resistance. For example, paper is impregnated with a VCI and placed in a polymeric bag containing the article to be protected.
Despite extensive use, typical corrosion inhibition processes such as the use of VCI's are not entirely satisfactory for all applications. For example, in the electronics industries it is often undesirable to have metal objects coated with an organic material. The disadvantage of coatings is particularly significant when the metal object is to undergo a treatment that is sensitive to contaminants. An exemplary situation involves the protection of lead frames utilized in the packaging of VLSI circuits. In such applications the lead wires from the VLSI chip are welded to the lead frame. This welding is not successfully accomplished in the presence of even a small amount of contaminant. If the lead frame is protected by a VCI, subsequent welding is prevented unless a meticulous and costly cleaning process is employed. Thus, for applications such as electronic chip manufacture the VCI's are not advantageous. As a result, these lead frames are generally not protected and corroded portions are removed before the lead frame is utilized. Although problems of contamination are avoided, substantial waste occurs.
In addition, in many applications such as the protection of ornamental objects or electronic structures, volatile corrosion inhibitors do not maintain their efficacy for a sufficient period of time. The duration of volatile corrosion inhibitor protection terminates soon after all the volatile organic material has evaporated from its carrying medium, e.g., the impregnated paper. Yet, this termination is not easily detected. Prompt steps cannot be taken to maintain corrosion inhibition. Thus, for applications that are sensitive to contamination or for applications requiring long-term protection, present methods of corrosion inhibition are often not acceptable.